1. Field of the Invention
The present invention relates to a spread illuminating apparatus of side light type, and particularly to a spread illuminating apparatus having a light conductor plate integrated with a housing frame.
2. Description of the Related Art
A liquid crystal display (LCD) device is small in profile, volume and weight, and therefore is extensively used in many kinds of electronic devices, such as a mobile telephone and a personal computer. Since a liquid crystal (LC) of the LCD device does not emit light by itself, an illuminating apparatus as lighting means to illuminate the liquid crystal is required when the LCD device is used in the dark environment where the sunlight or room light is not available. Also, since the LCD device, while increasingly downsized, is requested to have an enlarged screen size, it is required that the illuminating apparatus be reduced in size and also power consumption.
In order to reduce the size and power consumption of the illuminating apparatus, a point light source such as a light emitting diode (LED) is used as a light source of the illuminating apparatus, and the light source, light conductor plate and other constituent members of the illuminating apparatus are optimally arranged for an efficient utilization of light emitted from the light source.
For example, a spread illuminating apparatus of side light type shown in FIG. 7 includes LEDs 2 to emit light, a light conductor plate 1 having a rectangular shape and adapted to receive the light from the LEDs 2 and give out an illuminating light, and a housing frame 7 made of white resin and adapted to house the LEDs 2 and the light conductor plate 1 in place. Projections 12a and 12c are formed at each of side surfaces 11 and 12 of the light conductor plate 1 oriented orthogonal to an end surface 8 thereof having the LEDs 2 while recesses 20a and 20c are formed at each of inner side surfaces of the housing frame 7 oriented in parallel to the side surfaces 11 and 12 of the light conductor plate 1, and the projections 12a and 12c of the light conductor plate 1 engagingly fit respectively in the recesses 20a and 20c of the housing frame 7, whereby the light conductor plate 1 is firmly held in place inside the housing frame 7 (refer, for example, to Japanese Patent Application Laid-Open No. 2005-302485).
In the engagement structure described above, however, a predetermined gap must be provided between the light conductor plate 1 and the housing frame 7, and measures must be taken to compensate for loss of light which is caused by the presence of the gap. Also, since the reflectance ratio of the white resin of the housing frame 7 is smaller than that of a reflector composed of a reflection film, such as enhanced specular reflector (ESR) (refer, for example, to Japanese Patent Application Published No. H9-506837) thus causing loss of light, measures to compensate for such the light loss must also be considered. Further, when the engagement structure is subject to a further reduction in profile, its entire rigidity is lowered, and also the projections 12a and 12c of the light conductor plate 1 are likely to disengage from the recesses 20a and 20c of the housing frame 7.
In order to overcome the light loss, rigidity deterioration and disengagement problems found in the engagement structure of the light conductor plate 1 and the housing frame 7 shown in FIG. 7, an integral structure is proposed, in which, for the purpose of achieving a mechanical strength required for the entire unit while realizing a further profile reduction, a light conductor portion 421 and a housing frame portion 422 are integrated into a single piece as shown in FIG. 8, wherein the light conductor portion 421 includes a patterned area 426 located away from light sources 410 by a predetermined distance (refer, for example, to Japanese Patent Application Laid-Open No. 2006-285171).
In the integral structure shown in FIG. 8, since the housing frame portion 422 is made of the same resin material that is used for the light conductor portion 421 and therefore has a high light transmission rate, lights coming from the light sources 410 pass through the housing frame portion 422 and exit out therefrom. In order to prevent the light from exiting out through the housing frame portion 422, slit-like open spaces 425 to totally reflect the light from the light sources 410 are provided along the interface between the light conductor portion 421 and the housing frame portion 422. However, since polycarbonate or polymethylmethacrylate generally used as a resin material for the integral structure of the light conductor portion 421 with the housing frame portion 422 has a refractive index of around 1.5 thus meaning a relatively large critical angle, there may be a lot of lights that, depending on the structure design, impinge on the slit-like open spaces 425 at an angle smaller than the critical angle, which results in failure to prevent the lights from passing through the housing frame portion 422 and then exiting out.
Under the circumstances described above, if a reflection film is attached to the outer surface of the housing frame portion 422 for the purpose of preventing the lights from exiting out therefrom, the reflection film must be fixed to the housing frame portion 422 by using some appropriate method. For example, if a double stick tape is used for fixation, its adhesive layers undesirably absorb the lights. Even if the reflection film is duly fixed by any other methods than using a double stick tape, the lights are inevitably absorbed while going through the housing frame portion 422.